In recent years, mobile communication networks such as of cellular phones have been evolving rapidly. In particular, the third generation mobile communication systems based on W-CDMA (Wideband Code Division Multiple Access), UMTS (Universal Mobile Telecommunications System) and the like have been established rapidly in Japan and many other countries. The specifications of the third and following generation mobile communication systems are standardized by 3GPP (Third Generation Partnership Project).
In relation to the 3GPP standards, Non-patent Document 1 describes regulations concerning the Packet Data Convergence Protocol (PDCP). This PDCP is, for example, one of sublayers of the layer 2 in W-CDMA, and is a protocol including, as optional functions, a packet compression and decompression function, a cell re-selection function with no packet loss, and the like. PDCP is used, for example, in data communication between a base station device and a mobile station device, for the purposes of controlling the sequence of the communication and of keeping the communication data confidential.
In the specification “3GPP TS25.323, V3.3.0 (2000-09)” (Non-patent Document 1), for the purpose of controlling the sequence of data communication between a base station device and a mobile station device, PDCP is defined to perform window control by buffering 2048 pieces of data.
FIG. 16 is a schematic diagram for explaining general data processing using PDCP. As shown in FIG. 16, a core network device (backhaul) 600 sends data to a mobile station device (user terminal) 400 via a wireless base station device 500.
The wireless base station device 500 comprises a PDCP buffer unit 510 which is a buffer corresponding with PDCP. The wireless base station device 500 stores data sent from the core network device 600 temporarily into the PDCP buffer unit 510, and sends the data stored in the PDCP buffer unit 510 to the mobile station device 400. Here, as its specification is defined in the standard described in Non-patent Document 1, the PDCP buffer unit 510 is determined to have 2048 windows and not to be required to guarantee the volume of data exceeding the capacity of the windows.
In Japanese Patent Application Laid-Open No. 2009-89270 (Patent Document 1), described is a reference technology which is a communication system of an LTE (Long Term Evolution) method where a switching device sends data to a mobile station device via a wireless base station device.
Patent Document 1: Japanese Patent Application Laid-Open No. 2009-89270
Non-patent document 1: 3GPP TS25.323, V3.3.0 (2000-09)